Wow! Your Guest Book - Is Awesome!

OK.

I was on holidays (Porto Santo.. wonderful place! :D I will upload my photos on flickr sooner or later) and got back to work a couple of weeks ago. I sorted out comments just today.
In the next few weeks I will surely be busy because I have found a few ONLINE CHEAPEST PHARMACY with the “cheap cialis” I just needed and then I have so many porn and “teen amateur cams” to watch I just can’t get the time to read comments; so I (temporarily ?) disabled them. As soon as my penis is large enough thanks to the new techniques coming in every day, I will reenable them.
Now some notes to spammers :

1) Santa Maria Novella is a church in Ravenna (and a station in Florence), not a porn star (at least I hope there isn’t one).

2) “This is test-spam message, if you want stop spam on your site - just email me: xxxx@xxx.xx and your site will be immediately removed from spam-base.” Is not a good technique to get new mail addresses to be spammed, although we should never underestimate people stupidity… Beside, I think offering protection from spam using spam could be considered .. mafia.

3) If you translate your message in Italian, use a real translator. The following messages are not italian :

Scusilo,
voi compartecipe creativo luogo :D
Ci era un alberino e un autore come a legga circa:
Per trasmettere una Biglietti Auguri libera, scatti prego sopra una delle categorie cartoline scheda qui sotto. Saluti elettronici cartoline, mentre altri non possono caricarsi affatto auguri: frasi onomastico .. Luigi auguri di soggetti sms scrivere cartoline buon virtuali inviare lettera scaricare frasi d amore! Hm.. Noi non poteva scelga unico luoghi dove presenti, From questo link http://—–.com/ - frasi per laurea . Dal facciale in molle cartoline virtuali mia scusa attendente!

Saluti..
voi ottenuto piacevole fatto lavoro :-D
Qualcuno qui desideri a ritrovamento:
Gt materia cellulari dall gprs elettrico macchina sierosa giochi cellulare
Beta ed funzione insulto diabete diffusi cellulari vegetale! Hm.. Noi gradirebbe elimini favorevole pagine circa, From che del here http://—.com/ - cellulari symbian
Ammetta quello cercato male

That said, I would like to thank the two users posting real comments in these weeks and I will reply them soon. My real comments / spam ratio is then 0.2%. Wow.

August 3, 2007 | Filed Under Funny (maybe), Geeky side of life, Rants | Comments Off 

Unbelievable Optimization X

This is something which happened some years ago.

There was some-project I won’t name(*) (let’s just say it was a server emulator of some popular MMORPG), with their development forum. I found a post suggesting an optimization they were going to implement. Basically the file saving phase was something like this :


if (someplayer->hp != 0) fprintf(fout, "hp=%d", someplayer->hp);
if (someplayer->something != 0) fprintf(fout, "hp=%d", someplayer->something );
if (someplayer->foobar != 0) fprintf(fout, "hp=%d", someplayer->foobar );
if (someplayer->purplet != 0) fprintf(fout, "hp=%d", someplayer->purplet );
if (someplayer->dontknow != 0) fprintf(fout, "hp=%d", someplayer->dontknow );

Of course, most attributes were defaulting at 0 (or the value was different in the if — whatever) and many I/O operations were saved (also file length was greatly reduced due to this “optimization”). The reason of this high effectiveness was that most attributes were not used unless in a particular condition, and so most of the time they had a default value.

Comes the Pentium 4 and its light-years long pipeline.

Developers forums started writing about how crappy was the new architecture (the P4 debuted at 1.5GHz - at that speed it was slower than a P3 1GHz, not to mention the Athlon - the real power of the P4 was revealed only when it debuted a new revision and frequencies of 2.0GHz and above) and how much a single conditional jump could stall the pipeline and lose tiny precious clock cycles.

Then the idea struck a developer of that project. What if we remove all the if conditions ? No more conditional jumps yippieee!

This is the kind of ideas you feel dumber only hearing it. Ok, so you pull out the ifs and suddenly you have about double the number of fprintf. Since there is file caching (so that not particular much time is lost waiting for the disk I/O) the performances should be higher, right ? Wrong.
And the reason is simple. A single fprintf may be something like hundreds of conditional jumps. Really. (Not to mention the additional load in terms of disk I/O which whatever superscsi you have, it’s slower than the slowest of the P4s)

Let’s analyze (lightly) what happens on a call to fprintf. After all the arguments are pushed on the stack, the procedure is called. Here the format string is parsed to find the % sign. There is comparison/conditional jump for every character, but we can be sure that most of this conditionals are correctly predicted and only a fraction of them are mispredicted (probably the ones where the % is found). After the % char is found, a quite complex loop (thus involving a number of conditional jumps) parses the input string. For %d tokens this loop ends quite quickly but for more complex tokens this can be quite expensive. In the meantime, parsed characters were being passed to the file buffers, ready to be written out (we’ll see later what this means). When the %something token is parsed, the argument is written out to the disk. This involves things like sign extension and stuff like that and no, most of it (in Visual C++ RTL at least) is not done using movsx and alikes, but with slow C code using various if, to mantain compatibility across platforms (the VC++ RTL should run on x86, x86/64, IA64, Alpha, Mips and PowerPC, even if the support for most of the listed architectures is now dropped) . After this a number should be converted from the internal representation to the decimal one, and this involves a bazillion of jumps and divisions by 10 (in M$ Visual C++ you can see all this code in the crt/src/output.c file). After the string is prepared it’s stored in the files buffers. Overflows checks must be made (more jumps! and memory copies, with an high chance of trashing what is in L1 cache if not even L2) and when they are emptied (and sooner or later they will be) controls goes to ring-0 code. Apart from the jumps, going to ring-0 is an uber-slow operation in itself. Also ring-0 code has quite an high chance of accessing a resource which needs a synchronization lock with an high chance of a spinlock loop or, worse, an anticipated task switch.

But boy, you saved a conditional jump.

(*) There is a secret hint hidden in the post about the identity of this project…

Edit : I wrote Pentium 4 1.5MHz :D. While it would be funny to check if the P4 1.5MHz could beat the 8086 at 4.77MHz or the 286 at 8-12Mhz, usually Pentium 4 users runs them slightly faster ;)

October 21, 2005 | Filed Under C++, Programming, Rants, Uncategorized | 1 Comment 

I am too old

You may feel young when you love so much of the music around this year (Gorillaz, Oasis, Green Day, Coldplay, Kasabian, Garbage) that you really can’t choose which one should be your personal favorite of the 2005.

Then you discover that at the top of the BBC top ten charts there is a phone ring.

I’m too old to understand :(

May 31, 2005 | Filed Under Rants | Comments Off 

← Previous Page